Automated car washing machines typically include a drying apparatus which includes a blower and nozzle system arranged to direct air under pressure against the outer surfaces of a vehicle after the washing and rinsing operations have been finished, so as to strip water off the outer surfaces. Examples of such drying devices are shown in U.S. Pat. Nos. 5,535,475; 5,421,102; 4,969,272; 4,700,426; 4,589,160; 4,161,801; and 2,448,834. Each of the aforementioned patents shows a drying apparatus in which a plurality of air nozzles are arranged along a path of travel of the vehicle through the apparatus. The nozzles are so arranged that the drying process begins generally at the top front of the vehicle and proceeds generally downward and rearward toward the bottom sides of the vehicle. In this manner, water is progressively moved downward and rearward along the vehicle surfaces so that it eventually is blown or falls off the outer surfaces. This manner of arranging the nozzles provides an efficient stripping of water from the vehicle surfaces.
However, even with this type of nozzle arrangement, there remain at least two significant problems that are not solved by the apparatus in the aforementioned patents. First, in conventional drying apparatus such as shown in the aforementioned patents, water that is stripped from the vehicle falls or is blown onto the floor upon which the vehicle is supported. Because stripping of water from the surfaces requires that air be directed at high velocity in a generally downward direction toward the floor, water which is lying on the floor is often splashed by the high velocity air streams back up onto the vehicle. This results in inefficient drying because the same water is continually being stripped from the vehicle, redeposited onto the vehicle, restripped, and so on. This may also lead to incomplete drying, that is, water droplets remaining on the vehicle even after the vehicle has exited the drying apparatus. With such apparatus, the owner/operator of the car wash typically employs attendants who manually wipe the remaining water from the vehicle; alternatively, such as in some self-serve car washes, no manual wiping down of the vehicle is provided, resulting in an inferior result. Thus, with the conventional drying apparatus, the owner/operator either must incur labor costs which partially defeat the advantages of an automated car wash, or must accept inferior results.
A second problem that is not solved by the apparatus shown in the aforementioned patents is that even with a nozzle arrangement that efficiently strips water from the vehicle surfaces, inevitably some very small water droplets cannot be blown off the surfaces. For these very small droplets, the surface tension between the droplets and the vehicle surface exceeds the aerodynamic force imparted on the droplets by the air streams from the nozzles. In order to remove these small droplets, they must be evaporated. The rate of evaporation of a water droplet is highly dependent on ambient conditions, particularly the ambient temperature and relative humidity of the air surrounding the droplet. A drying apparatus for an automated car wash must be capable of evaporating small water droplets over a wide range of ambient conditions. Forcing high velocity air over the droplet increases the rate of evaporation, by lowering the vapor pressure of the air immediately adjacent to the droplet. Although forced air alone may be capable of completely evaporating the water droplets remaining on a vehicle surface given enough time, the high vehicle throughput rates that must be maintained in an economically practical car washing operation do not permit a vehicle to remain in the drying apparatus long enough to evaporate the water droplets using forced air alone, especially under extreme atmospheric conditions of, for example, 100 percent relative humidity and 90 degrees F.
One solution to this problem which has been proposed is shown in U.S. Pat. No. 2,663,951 issued to Kennison. That patent shows a drying apparatus in which hot water radiators are positioned with a blower within a casing so that the blower draws air over the radiators and then delivers the heated air to the nozzles. Heating the air is beneficial in increasing the evaporation rate. However, the apparatus shown in the Kennison patent suffers from two disadvantages. First, the intakes to the casing containing the radiators and blower are positioned close to the vehicle within the building which houses the car washing and drying apparatus. The result is that with continued use of the drying apparatus, water is continuously being evaporated into the air within the building, and the relative humidity within the space surrounding the vehicle will approach 100 percent even though the relative humidity outside the building may be significantly lower. Second, in a high flow rate air system, only modest increases in air temperature can be achieved with hot water radiators. Thus, Kennison notes that with his drying apparatus, one or two men are still required to remove water which remains on the vehicles after they have exited his apparatus.